Frequency selective acoustic mine firing control system



Dec. 12, 1961 c. B. BROWN ET'AL 3,012,503

FREQUENCY SELECTIVE ACOUSTIC MINE FIRING CONTROL SYSTEM Filed May 25,1944 2 Sheets-Sheet 1 JYQl.

Dec. 12, 1961 c. B. BROWN ETAL 3,012,503

FREQUENCY SELECTIVE ACOUSTIC MINE FIRING CONTROL SYSTEM Filed May 25,1944 2 Sheets-Sheet 2 B. Brown Paslay m: 5 Mm 2 1r E w 8 2. E mm 2 2 mmmm? B :F B n. .n w mm mm mm States Patent 'Cfifice 3,012,503 PatentedDec. 12, 1961 22 Claims. (Cl. 102-18) (Granted under Title 35, US. Code(1952), sec. 266) This invention relates to mine firing control systemsand more particularly to an acoustic mine firing control system forunderwater mines wherein the system operates to detonate and explode themine associated therewith when signals of predetermined character arereceived through the Water from sound emitting bodies such as surfacevessels, submarines, or the like, and the system operates to prevent afiring of the mine when signals of diiferent character are received aswhen heavy explosive charges are exploded adjacent to the mine or whenmine sweeping apparatus is operated within the vicinity thereof.

In acoustic mine firing control systems for underwater mines, itgenerally has been the practice to employ sound responsive devicesadapted to be actuated by sound waves or vibrations transmitted throughthe water in which the mines are placed, the sound responsive devicesbeing adapted, when actuated, to initiate the operation of apparatusadapted either to fire the mines, to respond insufiiciently to fire themines, or to prevent the firing thereof, as the case may be, dependingupon the character of the signals received. In any case, when signals ofpredetermined character are received by such a mine from a soundemitting body adapted to be destroyed by the mine, the operation of thesystem is timed in such a manner as to fire the mine when the body hasapproached within the zone of greatest effectiveness of the mine.

In certain of the prior art systems, electric contact actuatingapparatus comprising a plurality of contacts is employed wherein a firstpair of the contacts is adapted to be actuated by sound waves or pulsesof predetermined character such, for example, as those produced by avessel, thereby to control the operation of a mine firing circuit, and asecond pair of the contacts is adapted to be actuated by sound waves orpulses of different character such, for example, as explosion waves,thereby to prevent the first pair of contacts from controlling thefiring circuit when such different sound waves or signals are received.Thus, by this arrangement, a certain measure of protection ordiscrimination against signals not adapted to produce a firing actuationof the system is provided. In accordance with such arrangement, a timedelay device is usually employed to continue the control provided by thesecond pair of contacts. for a predetermined interval of time, therebyto render the firing circuit inoperative until the aforesaid differentsignals have died out in the acoustic field or zone or receptivity ofthe mine.

In certain other of the prior art systems, micro-telephonic devices areemployed to initiate the operation of' intermediate devices adaptedgradually to close a mine firing circuit in response to signals receivedfrom a vessel adapted to be destroyed by the mine employing the system.By reason of the gradual action in closing/the mine firing circuit, thesystem is caused tobegin itso'per ation while the vessel is at arelatively great distance from the mine, thereby to fire the mine onlyafter a period of time sufiicient to bring the vessel close enough tothe mine to destroy or effectively damage the vessel. Such anarrangement affords a further advantage in that it precludes a firing ofthe mine by the explosion of shells or bombs in its vicinity, soundwaves or pulses caused by such explosion being momentary only andentirely too brief to effect a firing actuation of the system.

In the arrangement of the present invention, an acoustic mine firingcontrol system is provided which possesses all of the advantages of theprior art systems and employs additional devices and circuitarrangements Whereby the system 'is rendered more critically responsiveto signals of predetermined character adapted to produce a firingactuation of the'system, and the system provides a higher degree ofanti-countermine and anti-sweep protection than that afforded by theprior art systems.

In accordance with the present arrangement, a soun responsive device isemployed, which device is adapted to convert underwater vibration in therange from fifty cycles per second to several thousand cycles persecond, for example, to electrical signals corresponding therewith. Theelectrical signals generated are applied to a firing control channel anda protective or discriminating channel adapted to pass respectively,signals within the entire range of signal frequencies and those signalsresidentin the range above a predetermined frequency therein. Each ofthe channels comprises a vacuum-tube amplifier, and electrical filtersassociated therewith whereby the firing channel is set for maximumsensitivity over a range of signal frequencies from fifty to one hundredand fifty cycles per second, for example, and the protective chan-. nelis set for maximum sensitivity in the range above one thousand cyclesper second, for example.

The arrangement of each of the amplifier tubes is such that the DC.voltage on the plate thereof is adapted to vary in accordance with thesound envelope of the acoustic energy reaching the sound responsivedevice. In the case of each of the amplifier tubes, the DC. voltagethereon is adapted to control the firing of a trigger tube ofthe coldcathode gas type. The trigger tube in the firing channel, when fired, isarranged to discharge a condenser through the detonator of the system,thereby to cause a firing operation of the system. "The trigger tube ofthe protective channel, however, when fired, is

arranged to discharge the condenser, thereby to prevent of time arecaused to elapse before plate voltages of sufii cient value to operatethe respective trigger tubes are developed by the amplifier tubescorresponding thereto. The relation of the time delays in the respectivechannels is set so that received signals having a frequency content andamplitude sufiicient to actuate both chan-i firing when subjected tosignals originating from any source not adapted to cause an explosion ofthe mine.

A coupling circuitris provided between the amplifier and trigger tubesof the firing channel, which coupling .cuit comprises a condenser and adischarge path therer adapted to prevent the application of a firingvoltage the trigger tube when the rate of increase of signals ceived bythe sound responsive device is below a pre- :termined value. Thecoupling circuit also provides l arrangement whereby a static biasvoltage is applied the trigger tube. Thus, by reason of the coupling'rangement, loud vessels approaching the mine at a stance therefrommerely cause an increase in the DC. ate voltage on the amplifier tubewithout increasing e voltage above the static voltage on the triggertube itil the vessels move within the zone of destructivity F the minewhereupon the rate of increase of signals :ceived from the vesselsincreases to such an extent that 1 operating bias is applied to thetrigger tube. Morever, it readily will be understood that, for the sameream, sweep apparatus operating at a safe distance from 1e mine will beunable to cause a firing actuation thereof. Anti-sweeping protectionalso is obtained to some tent by the aforesaid selection of signalfrequencies :lapted to actuate the firing channel for the reason thatveep apparatus heretofore deemed suitable for sweeping lines of the typeconsidered herein is not adapted to prouce signal frequencies within theselected range at a itisfactory level for safe sweeping. Moreover,addional protection is afforded by the protection channel 'hich operatesto prevent a firing actuation of the sys- :m when the sweep apparatusproduces a high proporon of high frequency signals.

An arrangement is provided whereby the sensitivity of le firing controlchannel may be adjusted at will to ny one of a plurality of signalslevels. In addition, the haracter of the amplifier tubes employed issuch as to ause variations in the sensitivities of different minesmploying the firing control system of the present invenon. Accordingly,in practice, such mines may be set zith a wide variety of sensitivitiesthereby to provide a 16881116 of discrimination against ships whichproduce ifferent noise levels and to render the sweeping of such ninesmore difficult.

According to the mine firing control system of the resent invention, theelements or component parts there- If comprise static elements such, forexample, as crystal microphones, electronic tubes, and condensers andreistors, which elements are not critically susceptIble to lamage causedby shocks associated with the launching if a mine. Accordingly, thesystem of the present inention is well adapted for use with minesadapted to re launched from an aircraft in flight.

An object of the present invention is to provide an LCOUStiC mine firingcontrol system for underwater mines, vhich system is rendered morecritically responsive to ignals of predetermined character than likesystems eretofore proposed for the purpose.

Another object in an acoustic mine firing control sysern is theprovision of new and improved anti-counternine and anti-sweep protectionfor underwater mines :mploying the system.

Another object is the provision of a new and improved 1CO1JStiC minefiring control system in which the system Jperates in response tosignals of predetermined character to actuate a mine firing controlcircuit and operates 11 response to signals of different character toprevent :he operation of such circuit.

Another object is the provision of a new and improved acoustic minefiring control system in which the system operates to produce a firingactuation thereof only In response to signals which increase at apredetermined rate and reach a predetermined degree of strengt Anotherobject in an acoustic mine firing control system is the provision of afiring control channel and a protective channelfor preventing a firingactuation of the system in which the protective channel is caused tooperate first when signals adapted to actuate both. of the channels arereceived by the system. i

Another object of the invention is the provision of a frequencyresponsive mine firing control system in which a single sound responsivedevice is employed to initiate a firing actuation of the system whensignals of predetermined frequency are received thereby and to cause thesystem to operate in such a manner as to prevent a firing actuationthereof when signals of difierent frequency are received thereby.

A further object is the provision of an acoustic mine firing controlsystem for underwater mines in which the system operates to fire themines in accordance with the character of the sound envelope of theacoustic energy reaching the mines from a sound emitting body movingwithin the vicinity of the mines.

A still further object in a frequency responsive mine firing controlsystem is the provision of a firing channel and a protective channel inwhich the maximum sensitivity of the firing channel is set within apredetermined range of frequencies and the maximum sensitivity of theprotective channel is set within a range of frequencies outside saidpredetermined range.

Still another object in an acoustic mine firing control system is theprovision of new and improved means for varying the sensitivity of thesystem.

A still further object in an acoustic mine firing control system forunderwater mines resides in the provision of new and improved means forcausing the DC. plate voltage on an amplifier tube to vary in accordancewith the sound envelope of the acoustic energy received by the systemthrough the water and to fire a trigger tube in accordance with suchvoltage variation.

An additional object in an acoustic mine firing control system in whicha trigger tube is fired in accordance with signals of predeterminedcharacter received by the system is the provision of new and improvedmeans for maintaining a static bias on the trigger tube.

Still other objects of the invention, not specifically set forthhereinabove, are those inherent in or implied from the novel combinationand arrangement of parts as will become more clearly apparent as thedescription proceeds, reference being had to the accompanying drawingswherein:

FIG. 1 is a sectional view with certain parts in elevation of anunderwater mine suitable for use with the acoustic mine firing controlsystem of the present invention; and,

FIG. 2 illustrates in diagrammatic form a complete circuit suitable foruse with the mine of FIG. 1 according to a preferred embodiment of theinvention.

Referring now to the drawings for a more detailed description of theinvention, and more particularly to FIG. 1 thereof, the numeral 10generally designates an underwater mine adapted to be launched from anaircraft in flight and adapted to come to rest on the bed of a body ofwater in which the mine is planted. The mine comprises an outer casing11 generally of cylindrical configuration and having a reduced endportion to which fins 12 or the like are secured to steer or guide themine in flight.

The casing 11 is divided internally at the reduced end portion thereofby a bulkhead 13 which supports a well 14 for a purpose hereinafter to.be disclosed. The casing 11 is also provided with inwardly extendingwells 15 and 16 from which extend respectively, tubesor ducts 17, 18 tothe bulkhead 13. The casing is further provided with a well 19 in whicha percussion detonator may be inserted, if desired, when the mine 10 isto be used for purposes other than those disclosed herein. Accordingly,for purposes herein, the well 19 is sealed as by a plug The remainingspace within the main portion of the casing 11 is filled with anexplosive charge 22 of TNT or the like sufficient to destroy or damage avessel and to impart a negative degree of buoyancy to the mine wherebythe mine is caused to sink through the water and come to rest on the bedthereof. The explosive charge conveniently may be admitted into thecasing by way of a suitable water tight filler opening 23.

A booster charge 24 and the extender mechanism 25 usually associatedtherewith are arranged within the well in watertight relation therein.The extender mechanism carries an electro-responsive detonator 26 forigniting the booster charge 24 and is adapted to move the detonator intooperative engagement with the booster charge when the mine reaches apredetermined depth of submergence in the Water, as is well known in theart to which this invention appertains. The leads 27 of the detonatorcomprise a cable 28 which is extended through the duct 17 to the reducedend portion of the casing 11.

Arranged within the well 16 in watertight relation therewith, is a clockmechanism 29 adapted to complete certain circuits of the electricalsystem within predetermined intervals of time after the mine has beenlaunched within the water, as will appear more clearly as thedescription proceeds. For this purpose, a multiconductor cable 31connected to contacts comprising the clock mechanism is extended throughthe duct 18 into the reduced end portion of the casing.

The well 14 serves as a housing and support for a battery 32, thebattery being clamped within the housing against a resilient support 33therein by means of a retaining ring 34 secured to the bulkhead as by aplurality of studs 35. The battery 32 is arranged to supply electricalenergy to a firing control mechanism 36 by way of a multi-conductorcable 37 when the aforesaid certain circuits have been closed by theclock mechanism 29 as explained in the foregoing.

The mechanism 36 is supported on the studs 35 by means of a plurality offlexible spacer plates 38, which plates may be formed of any suitablematerial such, for example, as wood, the plates being supported on thestuds and shaped to conform to the end portions of the mechanism. Thefree end portions of the studs 35 extend through and are supported by aplate 39, which plate is shaped to conform slideably with the innersurface of the casing 11. The projecting portions of the studs arethreaded to receive a plurality of nuts 41 whereby the mechanism 36 maybe clamped between the plates 38 when the nuts are drawn up tightagainst the slideable plate 39, substantially as shown.

The reduced end portion of the mine casing, at the open end thereof,carries a ring member 42 which is secured to the casing as by welding orotherwise suitably secured thereto. A dish-shaped cover 43 is secured tothe member 42 in watertight relation therewith as by a plurality ofscrews 44 carried by the flange portion 45 of the cover. The cover isprovided with a central opening 46 for receiving a sound responsivedevice 47. The device 47 is provided with a flange 48 by means of whichthe device is secured, as by a plurality of screws 49, to the cover, asuitable gasket 51 being inserted between the cover and the flange toinsure a watertight connection therebetween.

The sound responsive device 47 is of a type adapted to generateelectrical signals in accordance with sound waves or vibrations receivedthereby through the water in which the mine MP is placed, the devicepreferably being adapted to give a substantially flat response over awide range of signal frequencies such, for example, as fifty to twothousand cycles per second. For this purpose, the device 47 may be ahydrophone of any well-known type suitable for the purpose, butpreferably is of a type comprising crystal microphones for the reasonsthat such a hydrophone is mechanically strong, has a substantiallyconstant sensitivity notwithstanding the depth of submergence of thehydrophone within the water, and is relatively smaller in size thanother hydrophones capable of equivalent performance.

Crystal hydrophones of the type employed herein'are Well known in theart. Accordingly, a brief description of a device suitable for thepurpose herein will suflice. The hydrophone 47 preferably comprises aplurality of crystals such, for example, as Rochelle salt crystals,which crystals are cemented between a cast iron housing and a steeldiaphragm. Pressure from the surrounding water is transmitted to thediaphragm through an outer rubber housing secured to the cast ironhousing and thence through a suitable type of oil such as castor oildisposed between the diaphragm and the rubber housing; A small hole isprovided in the diaphragm by means of which hole hydrostatic equilibriumis established between the rubber and cast iron housings.

The electrical signals generated by the hydrophone 47 are applied to thefiring control mechanism 36 by way of a cable 52. The free end of eachof the cables 28, 31, 37, and 52 carries a plug or jack adaptedinterfittingly to engage a counterpart therefor carried by the firingcontrol mechanism 36, thereby to provide an arrangement whereby theelectrical connections of the system are facilitated when the mine isassembled. It will be understood, of course, that all necessary openingsin the spacer plates 38 and the supporting plate 39 are provided toaccommodate the extension of the cables therethrough.

The firing control mechanism 36 comprises a firing channel adapted tofire the detonator 26'when operation of the mechanism is initiated bythe sound responsive device 47 in response to signals of predeterminedfrequency received thereby. The control mechanism 36 also comprises aprotective channel adapted to prevent firing of the detonator whenoperation of the mechanism is initiated by the sound responsive device47 in response to signals of difierent frequency received thereby. Eachof the firing and protective channels comprises, among other elements,an amplifier detector tube of the electron discharge type and a coldcathode type trigger tube controlled thereby, as will appear in greaterdetail as the description proceeds.

The operation of the firing control system of the mine 10 and thearrangement of the several electrical components thereof best will beunderstood by reference to FIG. 2 of the drawings wherein the electricalsystem of the mine is shown diagrammatically.

The firing mechanism 36 comprises a firing control channel and aprotective or countermine channel designated generally by the numerals53 and 54 respectively. The firing control channel comprises anamplifier-detector tube 55 of the electron discharge type and a coldcathode gas type trigger tube 56 controlled thereby. The protectivechannel similarly comprises an amplifier-detector tube 57, which may beidentical to tube 55 of the firing channel, and a trigger tube 58controlled thereby, tube 58, if desired, being identical to trigger tube56 of the firing channel.

The amplifier-detector tubes 55, 57 each comprises a plate or anode 59,a combined cathode-filament'La suppressor grid '62 connected to thecathode in the usual manner, screen grid 63, andcontrol grid 64, whichelements comprise the amplifier circuit of the tubes. Each of tubes 55,57 also comprises a detector circuit which in cludes the plate 65 andcathode 61. The function of the detector circuit, as will appear ingreater detail hereinafter, is to apply an increasing negative bias tothe control grid 64 in response to A.C. signals of predeterminedcharacter applied thereto, thereby to increase the potential on theplate 59 in proportion to said applied A.C. signals.

.Each of the trigger tubes 56, 58 comprises a plate or anode 66, acathode 67, and a control grid 68. ,With a potential of lSO'volts, forexample, between the. plate 66 and cathode 67 of each of the triggertubes 56, 58, each tube is fired or triggered when a potential such, forexample, as 70 volts is applied to the control grid thereof.

. Each of the control grids 63, however, normally is main tained at astatic or non-firing bias such as 55 volts,

)r example, in a manner to appear in detail hereinafter. he rise inpotential above the static bias on each of 1e trigger tubes 56, 58 iscontrolled by the rise in poantial on the plates 59 of the amplifiertubes 55, 57 repectively associated therewith. For this purpose, thelate 59 of tube 55 is coupled by way of a condenser 9 and a resistor 71to the control grid 68 of trigger be 56. In like manner, the plate 59 ofamplifier 57 is oupled by way of a condenser 72 to the control grid 8 oftrigger tube 58.

The operating voltages for the amplifier and trigger ubes are providedby the battery 14 which comprises a t-battery section 73 and anA-battery section 74, the ow voltage sides of which sections aregrounded at 75. The A-battery section 74 supplies the filaments 61 of,mplifier tubes 55, 57, the filaments being grounded on me of the sidesthereof and connected on the other sides hereof to the high voltage sideof A-battery section 74 )y way of contacts 76, 77 of the clock mechanism29. Fhe high voltage side of B-battery section 73 is applied the plates59 of the amplifier tubes 55, 57 by way of :ontacts 78, 79 of clockmechanism 29 and plate load 'esistors 81, 82 of control channels 53, 54respectively. Fhe screen grids 63 of amplifier tubes 55, 57 aremainained at the potential provided by a low voltage tap 3 of theB-battery section 73, and the screen grid 63 )f tube 55 is stabilized atthis potential by means of a :ondenser 84 connected between the screengrid'and ground in a well known manner.

The plates 66 of trigger tubes 56, 58 are connected by avay of aresistor 85 to a high voltage tap 86 provided an the B-battery section73, the voltage thereat being maintained on a condenser 87 connectedbetween the plates '66 and ground, which condenser obtains the charge:hereon by way of resistor 85. The cathode 67 of trigger .ube 56 isconnected through contacts 88, 89 of clock nechanism 29 and detonator 26to ground potential 75. Cathode 67 of trigger tube 58 is connected byway of a protective resistor 91 to ground potential at 75.

The aforesaid static biases applied to the control grids 68 of triggertubes 56, 58 are provided by means of a voltage divider networkcomprising resistors 92, 93 connected in series across the portion ofthe B-battery section 73 between the high voltage side thereof and lowvoltage tap 83 thereon. The voltage at the junction of resistors 92, 93is applied through resistors 94 and 71 to the control grid 68 of triggertube 56 in the firing channel. In like manner, the voltage at thejunction of resistors 92, 93 is applied by way of a resistor 95 to thecontrol grid 68 of trigger tube 58 in the protective channel.

The A.C. signals generated by the hydrophone 47 are applied through acondenser 96 to an attenuator network comprising resistors 97, 98, 99,and a condenser 101 shunted across the resistor 99. These resistors andcondensers comprise the input to the firing control channel 53.Condenser 96 is selected to pass without attenuation electrical signalsover the aforesaid frequency range of 50 to 2000 cycles per second.Resistor 97 is also con nected to the fixed contacts 102, 103 of amanually adjustable sensitivity switch 104 the wiper or switch arm 105of which is electrically connected to the control grid 64 ofamplifier-detector tube 55.

By reason of the provision of sensitivity switch 104 the maximum A.C.input appearing across the attenuator network may be applied to thecontrol grid '64 when the wiper arm 105 is moved into engagement withthe contact 102 of switch 104. Or, when desired, the firing channel 53may be rendered less sensitive by moving the wiper 105 into engagementwith the contact 103, in which case, a relatively larger input signalvoltage is required across the attenuator network to fire the triggertube 56.

in any case, the A.C. voltages applied to the control grid 64 ofamplifier tube 55 are amplified in the amplifier plate circuit thereof.The high frequency content of the amplified signals appearing at plate59 of amplifier tube 55 are by-passed to ground through a condenser orfilter 106 such that the firing control channel 53 is caused to give amaximum sensitivity within the frequency range from 50 to 150 cycles persecond, for example. The amplified signals in this frequency range passthrough a condenser 107 and the detector circuit comprising plate 65 andcathode 61 of amplifier-detector tube 55, thereby to rectify suchsignals. The rectified current flows through the resistor condensercombination 99, 101 and a resistor 108, thereby charging condenser 101negatively with respect to ground. The negative potential developed oncondenser 101 is applied as negative bias on the control grid 64 of tube55 by way of resistors 98, 97 or resistor 98, as the case may be,depending upon the instant position of wiper of sensitivity switch 104.

The condenser resistor combination 101, 108 is selected to provide atime constant or delay such that the bias developed on the control grid64 of tube 55 causes a rise in the D.C. potential on plate 59 thereof,which rise in potential is proportional to the sound envelope of theacoustic energy received by the hydrophone 47 from a vessel of a typeadapted to be destroyed by the mine 10.

The condenser resistor combination 69, 94 comprising the couplingbetween the tubes 55, 56 provides an arrangement whereby the signalenvelope of the sound reaching the hydrophone 47 is required to increaseat a rate which exceeds the rate of discharge of the condenser 69through the resistor 94. Thus, the trigger tube 56 is fired only whensignals within the aforesaid frequency range of 50 to 150 cycles persecond are received by the hydrophone 47 and only when such signalsreach a predetermined degree of strength and increase at a rate whichexceeds the discharge rate constant of condenser resistor combination69, 94.

The A.C. signals generated by the hydrophone 47 also are applied througha condenser 109 to an attenuator network comprising resistors 111, 112,113, an adjustable resistor 114, and a condenser shunted acrossresistors 113 and 114, these resistors and condensers comprising theinput to the protective channel 54. Resistor 111 is also connected tofixed contacts 116, 117 of a sensitivity switch 118, the wiper 119 ofwhich is electrically connected to the control grid 64 of amplifier tube57 and is mechanically coupled to the wiper 105 of switch 104 asindicated by the dash line 121 therebetween. Accordingly, it will beunderstood, wiper 1 19 of switch 118 is caused to engage contact 116thereof when the wiper 105 of switch 104 engages the contact 102thereof. Also, when the wiper 104 of switch 105 is caused to engagecontact 103 thereof, the wiper 119 of switch 118 is caused to engagecontact 117 thereof.

The condenser 109 is selected to give the protective channel a maximumsensitivity above the range of 1000 cycles per second, for example, andthe sensitivities of the channels with respect to the signal levels atthe attenuator networks individual thereto are rendered adjustable withrespect to each other by means of the adjustable resistor 114. Inpractice, for example, the ratio of the signal input at 100 cycles persecond required to cause firing of the trigger tube 56 of the firingcontrol channel to the signal input at 2000 cycles per second requiredto cause firing of the trigger tube 58 of the protective channel ispreferably such that the protective channel affords a slightly greatersensitivity. Thus, when sound signals are received by the hydrophone 47,which signals have a frequency content, and signal level critical to theactuation of both channels, the operation of the protective channelisinsured, thereby to prevent a firing actuation of the firing controlsystem. It will be understood, of course, that the adjustable resistor114 may comprise an element. of the attenuator network of the firingcontrol channel rather than that of the protective channel or each ofthe networks may comprise an ad- 7 justable resistor, if desired.

As in the case of amplifier tube 55 of the firing control channel, A.C.signals appearing on the control grid 64 of the amplifier tube 57 areamplified in the plate circuit thereof and appear at the plate 59 of thetube. The amplified A.C. signals pass through a condenser 122 and thedetector circuit comprising plate 65 and anode 61 of tube 57, suchsignals being rectified by reason of the detector circuit. The rectifiedcurrent flows through the condenser resistor combination 115, 114, 113and a resistor 123 and develops a change on condenser 115, which chargeis negative with respect to ground potential. The voltage on condenser115 is applied as negative bias on the control grid 64 of tube 57 by wayof resistors 112, 111 or resistor 112 as the case may be, depending onthe position of wiper 119 of switch 118. The time constant of condenserresistor combination 115, 123 is such that the negative bias developedon control grid 64 is caused to produce a rise in the DC. potential onplate 59 of tube 57, which rise in DC. potential is proportional to thesound envelop of the high frequency content of signals received by thehydrophone 47.

Thus, by reason of the foregoing arrangement, high frequency signalssuch, for example, as explosion waves caused by counter-mining producean actuation of the protective channel. The relation or ratio of thetime delays provided by condenser 101, resistor 108, and condenser 115,resistor 123 of the firing control and protective channels respectively,is arranged to be in the ratio of fifty to one, for example, such thatthe protective channel is caused to operate first in the event thatsignals having a frequency content critical to the operation of bothchannels are concurrently received by the hydrophone 47.

As in the case of the firing control channel, the condenser resistorcombination 72, 95 of the protective channel provides an arrangementwhereby a gradual rise of the D.C. potential on plate 59 of tube 57'does not produce a rise in potential above the static bias applied tothe control grid 68 of trigger tube 58, when the rate of such potentialrise does not exceed the time of discharge of condenser 72 throughresistor 95. Such an arrangement is desirable in that it prevents afiring of either of the trigger tubes 56, 58 in the event that the DC.potential at plate 59 of either of the amplifier tubes 55, 57 rises byreason of the aging of the tubes or by reason of a decrease in thebattery potential at the filaments 61 thereof.

Moreover, by making the product of the condenser resistor combination69, 94 large with respect to the product of the condenser resistorcombination 72, 95, countermine protection operation is prevented whenthe amplitude of the incoming signal is rising slowly even though thesignal is composed of high and low frequencies.

When trigger tube 56 is fired, a circuit is completed for dischargingcondenser 87 through the detonator 26, thus producing a firing actuationof the firing control system. However, when the trigger tube 58 isfired, a circuit is completed for discharging condenser 87 through tube58 and resistor 91, thus preventing the energization of detonator 26notwithstanding the subsequent appearance of a firing potential atcontrol grid 68 of trigger tube 56. The time constant of condenserresistor combination 87, 85 is such that sufiicient time is provided toallow for the cessation in the acoustic field of mine 10 of signalswhich initiate operation of the protective channel.

Having described the several electrical components of the control systemand the arrangement thereof, the operation of the system will now bedescribed. Let it be assumed that the mine 10 has been launched into abody of water and has come to rest on the bed thereof. Let it be assumedfurther that the extender mechanism has operated and moved the detonator26 into operative engagement with the booster charge 24 by placing thedeto- 1T0 nator within a cavity 124 formed Within the booster charge.Let it further be assumed that before the launching of the mine, thesensitivity switches 104, 118 have been moved into their full linepositions to provide a maximum sensitivity of the mine firing systemwhereby the mine 10 is adapted to respond to and destroy surfacevessels, or other sound emitting bodies, which transmit through thewater sound signals at a relatively low sound level and of a characteradapted to produce a firing actuation of the mine.

After an interval of time has elapsed during which a salt washercomprising an element of the clock mechanism 29 is dissolved, adiaphragm 125 comprising another element of the clock mechanism ispermitted to move under pressure of the surrounding water and toinitiate the operation of a spring wound motor, which motor drives a cam126 of the clock mechanism in a well-known .manner. The cam 126 ismounted for rotation on a pivot 127 and moves in the direction of arrow128 until the cam engages a stop pin 129 disposed within anarcuate slot131 provided in the cam. During this movement of the cam 126 theaforedescribed pairs of contacts of the clock mechanism 29 are adaptedto be closed in sequence. Each of the several pairs of contactscomprises a follower 132 of any suitable insulation material, whichfollower is urged'into engagement with a cylindrical cam surface 133provided on cam 126. The cam surface is provided with a plurality ofperipheral indentations 134, 135, 136 therein, which indentations areadapted to receive the followers 132 and are of varying lengths, therebyto cause the pairs of contacts to close in sequence.

According to the foregoing arrangement, contacts 76, 77 of clockmechanism 29 are the first to close. Closure of these contacts suppliesthe potential of the A-battery section 74 to the filaments 61 of theamplifier tubes 55, 57 by way of a circuit which may be traced asfollows: from the high voltage side of A-battery section 74 through aconductor 137, contacts 76, 77 of clock mechanism 29, a conductor 138,and thence through filaments 61 of tubes 55, 57 to ground potential atthe low voltage side of A-battery section 74.

After a predetermined interval of time, contacts 78, 79 of the clockmechanism 29 are closed, thereby to apply the potential of B-batterysection 73 to the plates 59 of amplifier tubes 55, 57 by way of acircuit which may be traced as follows: from the high voltage side ofB-battery section 73 through a conductor 139, contacts 78, 79 of clockmechanism 29, a conductor 141, and thence through the plate loadresistors 81, 82 to the plates 59 of amplifier tubes 55, 57respectively.

After a further predetermined interval of time, contacts 88, 89 of clockmechanism 29 are closed to complete a circuit between the cathode 67 oftrigger tube 56 and the detonator 26. This circuit includes cathode 67of trigger tube 56, conductor 142, contacts 88, 89 of clock mechanism29, and a conductor 143 connected between the contacts and the detonator26.

When the potential at the several points in the electrical systemreaches a stable or steady state condition, a potential of approximately30 volts appears at each of the plates 59 of the amplifier tubes 55, 57,a potential of approximately 55 volts appears at each of the controlgrids 68 of the trigger tubes 56, 58, and a potential of approximatelyvolts appears at each of the plates 66 of the trigger tubes.

In the event that a vessel which emits underwater sound Within thefrequency range of 50 to 150 cycles per second and at a higher levelthan sounds of other frequencies emitted by the vessel approaches themine 10 at a distance therefrom,'such sounds are received by thehydrophone 47 and produce a rise in the DC. potential at plate 59 ofamplifier tube 55, which rise in potential is proportional to the soundsignal envelope resident in the aforesaid frequency range and receivedby the hydrophone 47 as g he vessel approaches progressively nearer tothe mine 10. In the event that the sound envelope increases at a ratewhich corresponds substantially to the charging rate of :ondenser 101, aDC. voltage of approximately 45 volts appears at the plate 59 ofamplifier tube 55 at a time when :he vessel moves into the zone ofdestructivity of the mine it). The increase in the potential to 45 voltson one side of :ondenser 69 produces a corresponding increase in theaotential to 70 volts on the other side of the condenser, :hus applyingthe aforesaid firing potential of 70 volts on ;he control grid 68 oftrigger tube 56. When this occurs, :he trigger tube is fired and thecondenser 37 discharges :herethrough, thereby to energize the detonator26 by way of a circuit which may be traced as follows: from ane side ofcondenser 87 through a conductor 144, plate 56 and cathode 67 of triggertube 56, conductor 142, contacts 88, 89 of clock mechanism 29, conductor143, :letonator 26, and thence through a conductor 145 to groundpotential at the other side of condenser 87.

In the event that the approaching vessel is relatively noisy andproduces underwater sound at a high level such that a rise in potentialoccurs at the plate 59 of tube 55 while the vessel is still at arelatively great distance from the mine 10, the potential increases tooslowly to produce an increase in potential at the trigger tube side ofcondenser 69, the charge on condenser 69 being dissipated through theresistor 94 as the voltage on the opposite side of the condenserincreases toward the static voltage on the trigger tube side thereof.Accordingly, an increased voltage on condenser 69 sufficient to fire thetrigger tube 56 is not developed on the condenser until the vesselapproaches sufficiently near to the mine to cause a rise in potential atthe plate 59 of tube 55 at a rate which exceeds the discharge rate ofcondenser 69 through resistor 94. Thus, by reason of the arrangementprovided by the resistor condenser combination 94, 69, the zone withinwhich firing of the mine Will occur in response'to the presence of avessel therein is substantially narrowed. Moreover, in like manner,sweep apparatus which produces at a high level sound signals critical toa firing actuation of the firing control channel and which apparatus isoperated outside the zone of destructivity of the mine merely raises thepotential level at the plate 59 of tube 55 without producing an increasein the potential on the trigger tube side of condenser 69 suficient tocause a firing of trigger tube 56.

When it is desired to limit the response of the mine to relatively loudvessels, the sensitivity switch 104 may be adjusted such that the wiper105 thereof engages the fixed contact 103 in which position of theswitch a substantially greater AC. input is required across theattenuator network comprising the input of the firing control channel tocause a firing actuation of the channel, the operation of the channelotherwise being the same. It will be appreciated, of course, thatseveral mines adjusted for different sensitivities may be planted in agiven area and thereby provide response as a group to vessels producingdifferent sound levels. The character of the amplifier tubes also issuch as to cause a variation in the sensitivities of different mines,thereby to provide a wide variety of sensitivity settings therefor.

The condenser 106, as described in the foregoing, is selected to by-passall signals in the firing control chan nel 53 not adapted to produce afiring actuation thereof. However, in the event that a burst of energyproduces a sudden rise in potential at the control grid 68 of triggertube 56, the filter comprising the resistor condenser combination ofresistor 71 and a condenser 70 is provided to by-pass such transientsignals to ground potential, thereby to prevent a spurious andaccidental firing of the trigger tube 56.

In the event that an approaching vessel which produces underwater soundhaving a frequency content adapted to produce a firing actuation of thefiring control channel 53 also produces underwater sound having afrequency content above a frequency of 1000 cycles per second and whichsound is produced at substantially the same level as the sound residentin the first named frequency content, or in the event that sweepapparatus having the same sound producing capacity is operated withinthe vicinity of the mine 10, or in the event that heavy explosivecharges or a like mine is exploded within the vicinity of the mine 10,the high frequency waves or vibrations, however caused, are transmittedthrough the water to the hydrophone 47. The electrical signals generatedby the hydrophone, which signals correspond to the high frequency wavesreceived thereby, produce a rise in the D.C. potential at plate 59 ofamplifier tube 57 sufiicient to apply a firing potential on the controlgrid 68 of trigger tube 58, the potential rise on plate 59 of tube 57appearing well in advance of a rise in potential on plate 59 of tube 55by reason of the relation of the time delays provided in the channels,as described in the foregoing.

Firing of trigger tube 58 provides a discharge path for condenser 87therethrough by way of the protective resistor 91, thus rendering thefiring control channel ineffective to energize the detonator 26notwithstanding the subsequent appearance of a firing potential at thecontrol grid 68 of trigger tube 56. In case the firing of trigger tube58 has been caused by an explosion wave reaching the hydrophone 47, thecharging time of condenser 87 is such that sufiicient time is providedto permit the explosion levels to die out before a steady state orstable condition of the firing channel is established.

The character of the amplifier tubes 55, 57 is such that theamplification provided thereby is non-linear. Thus, when the DC.potential at the plate 59 of tube 55 is raised to a predetermined value,the DC. potential thereon does not substantially increasenotwithstanding a continuous increase in the AC. input applied to thecontrol grid 64 of the tube. Accordingly, sweep apparatus which producesunderwater sound at an unusually high level is unable to produce afiring actuation of the firing control channel notwithstanding that theincrease in such sound be at a rate otherwise adapted to produce suchfiring actuation.

From the foregoing, it should now be apparent that an acoustic minefiring control system has been provided which is well adapted to fulfillthe aforesaid objects of the invention. Moreover, it further should beobvious that the system, by reason of the static or non-moving characterof the component parts thereof, is well suited for use with a mineadapted to be launched from an aircraft in flight.

While the invention has been described in particularity with respect toan example thereof which gives satisfactory results, it readily will beapparent to those skilled in the art, after understanding the invention,that further embodiments and variations of the invention may be madewithout departing from the spirit and scope of the invention as definedby the appended claims.

The invention herein described and claimed may be manufactured and usedby or for the Government of the United States of America forgovernmental purposes without payment of any royalties thereon ortherefor.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. An acoustic mine firing control system of the character disclosedcomprising, in combination, a mine firing circuit, means for controllingthe operation of said circuit, a sound responsive device, meanscontrolled by said sound responsive device for operating said circuitcontrolling means when signals of predetermined character are receivedby said device, and means controlled by said sound responsive device forpreventing the operation of said firing circuit when signals ofdifferent character are received by the device.

2. In an acoustic mine firing control system of the character disclosed,the combination of a mine firing circuit, a sound responsive device, anda plurality of frequency selective circuits controlled by said deviceand 13 effective in response to a predetermined rate of increase ofsound signals in the selective frequency thereof reaching said devicefor selectively controlling the operation or hold-off of operation ofsaid firing circuit when signals having said predetermined rate arereceived by the device.

3. In an acoustic mine firing control system of the character disclosed,the combination of a mine firing circuit, a sound responsive device,impedance networks selectively responsive to signals of differingfrequency bands received by said device, which signals increase at apredetermined rate and reach a predetermined value, for selectivelycontrolling the operation or hold-off of operation of said firingcircuit when said signals are received by the device.

4. In a frequency responsive underwater mine of the character disclosed,the combination of a mine firing circuit, means responsive to soundsignals received through the surrounding water and having apredetermined frequency content for controlling the operation of saidfiring circuit, means responsive to sound signals received through thewater and having a frequency content dif ferent from said predeterminedfrequency content for preventing the operation of said circuit, andmeans for causing said preventing means to operate before said circuitcontrolling means operates when signals respectively adapted to operatesaid controlling and preventing means are received concurrently throughthe surrounding water.

5. In an acoustic underwater mine of the character disclosed, thecombination of a mine firing and protective within the vicinity of themine, a plurality of frequency selective channels including amplifyingmeans controlled by said sound responsive means for producing anelectrical signal which increases in value in proportion to the soundenvelope of acoustic energy reaching the sound responsive means from thesound emitting body, and trigger means controlled by said electricalsignal in each of said channels for causing a firing actuation of saidfiring circuit or a protection of said firing circuit against actuation,correlative with the frequency content of said sound signals withrespect to the predetermined selected frequency of said channels whenthe electrical signal increases at a predetermined rate and reaches apredetermined value.

6. In an acoustic mine firing control system, the combination of a minefiring circuit, means responsive to sound signals within a predeterminedfrequency range for causing a firing actuation of said circuit when saidsound signals are received by the sound responsive means, meansresponsive to sound signals of different frequency for preventing afiring actuation of said circuit when said signals of differentfrequency are received by said last named sound responsive means, andmeans for substantially equalizing the sensitivities of said actuatingand preventing means with respect to said signals individual thereto.

7. In an acoustic mine firing control system, the combination of a minefiring circuit, means adapted to receive sound signals and generateelectrical signals in accordance therewith, means controlled by saidelectrical signals and adapted to cause a firing actuation of saidcircuit when said electrical signals comprise signals within apredetermined range of frequencies, means controlled by said electricalsignals and adapted to prevent a firing actuation of said firing circuitwhen said electrical signals comprise signals within a different rangeof frequencies, means for substantially equalizing the sensitivities ofsaid circuit actuating and preventing means with respect to signalsindividual to the operation thereof, and means for causing saidpreventing means to operate first when signals adapted to initiate theoperation of both said circuit actuating and preventing meansconcurrently are generated by said sound receiving means.

8. In an acoustic underwater mine of the character disclosed, thecombination of a mine firing and protective circuit, means responsive tosound signals received from a sound emitting body approaching the mineat a distance therefrom, a plurality of frequency selective channelsincluding amplifying means controlled by said sound responsive means forproducing an electrical signal which varies in value in proportion tothe sound envelope of acoustic energy received from said sound emittingbody when the body approaches the mine at a predetermined speed, aplurality of trigger means controlled by said electrical signal in eachof said channels for causing a firing actuation of said firing circuitor a protection of said firing circuit against actuation, correlativewith the frequency content of said sound signals with respect to thepredetermined selective frequency of said channels when said electricalsignal reaches a predetermined value, and means settable at will todifferent settings for varying the sensitivity of said electrical signalproducing means thereby to produce a firing actuation of said firingcircuit when said electrical signal reaches a different predeterminedmagnitude and rate of increase.

9. In an acoustic mine firing control system, the combination of a minefiring circuit, a sound responsive device, means controlled by saidsound responsive device and efiective to cause a firing actuation of thefiring circuit a predetermined period of time after signals ofpredetermined character arereceived by said device, and means controlledby said sound responsive device and effective to prevent a firingactuation of said circuit a predetermined interval of time after signalsof character different from said first named signals are received by thesound responsive device.

10. In an acoustic mine firing control system, the combination of a minefiring circuit, means responsive to sound signals received therebywithin a predetermined range of frequencies, means controlled by saidsound responsive means for controlling the operation of said firingcircuit, means controlled by said sound responsive means for preventingthe operation of said firing circuit, means for providing said circuitcontrolling means with a maximum sensitivity with respect to signalsresidentin a portion of said frequency range, and means for providingsaid preventing means with a maximum sensitivity with respect to signalsresident in another portion of said frequency range.

11. In an underwater mine, an acoustic mine firing control systemtherefor, comprising, in combination, a sound responsive device adaptedto receive sound signals transmitted through the water, means controlledby said device for firing the mine a predetermined interval of time"after sound signals are received by the device from a sound emittingbody adapted to be destroyed by the mine, means effective when operatedto prevent the operation of said mine firing means during apredetermined interval of time, and means controlled by the soundresponsive device for initiating the operation of said preventing meansa predetermined interval of time after signals are received by the soundresponsive device from a sound emitting body not adapted to be destroyedby the mine.

12. In an acoustic mine firing control system, the combination'of a minefiring control circuit including a trigger device, a sound responsivedevice, an amplifier device controlled by said sound responsive deviceand adapted to produce an electrical signal which varies in value inproportion to the sound envelope of the acoustic energy reaching saidsound responsive device, and a coupling system, the combination of amine firing circuit, a plurality of frequency selective networks, asound responsive device, a plurality of amplifier-detector devicesconnected aoiases saidfrequency selective networks and controlled by aidsound responsive device and adapted to produce elecrical signals whichincrease in value in accordance with ound signals of predeterminedcharacter received by he sound responsive device, and a plurality oftrigger neans controlled by said electrical signals and for selecivelyrendering said circuit inoperative for protection hereof or to operatesaid firing circuit correlative to the frequency content of said soundsignals with respect to he selective frequency passed by respective onesof said irequency selective networks when said electrical signalsncrease at a predetermined rate.

14. In an acoustic mine firing control system, the comaination of a minefiring circuit, a sound responsive device, a firing control channelcontrolled by said sound responsive device and adapted to operate saidcircuit when signals of predetermined character are received by thesound responsive device, and a protective channel controlled by saidsound responsive device and adapted to prevent the operation of saidfiring circuit when signals of difierent character are received by saidsound responsive :levice, each of said channels comprising anamplifier-detector tube and a trigger tube controlled thereby.

15. In an acoustic mine firing control system, the combination of asound responsive device, a mine firing control channel controlled bysaid device, a protective channel controlled by said device, and meansindividual to each of the channels for respectively providing thechannels with maximum sensitivities which correspond respectively tosound signals critical to the operation of the channels.

16. In an acoustic mine firing control system, a sound responsivedevice, a mine firing control channel, a protective channel, adjustablemeans for varying at will the sensitivities of said channels withrespect to the sound level of acoustic energy received by said soundresponsive device, and means adjustable at will for substantiallyequalizing the sensitivities of the channels.

17. in an acoustic mine firing control system, the combination of a minefiring control channel, a protective channel, a sound responsive devicefor generating signals adapted to initiate the operation of saidchannels, time delay means individual to each of said channels forpreventing the operation thereof until a predetermined interval of timehas elapsed after sound signals critical to the operation of saidchannels respectively have been received by said sound responsivedevice, said time delay means being arranged in such a manner as tocause the protective channel to operate first when sound signalscritical to the operation of both channels concurrently are received bysaid sound responsive device.

18. In an acoustic mine firing control system, the combination of asound responsive device, a detonating device, a mine firing controlchannel responsive to signals of predetermined character received bysound responsive device for operating said detonating device apredetermined interval of time after said signals are received, aprotective channel responsive to signals of different character receivedby said sound responsive device and adapted to. be operated apredetermined interval of time after such different signals arereceived, and means controlled by said protective channel for preventingthe operation of said detonating device by said firing channel during apredetermined interval of time following an operation of the protectivechannel.

19. in an acoustic mine firing control system, the combination of a minefiring control circuit including a plurality of trigger tubes eachcomprising a plurality of elements including a control grid,amplifier-detector tubes each comprising a plurality of elementsincluding a plate, a source of electrical energy for supplying operatingelectrical potentials for the elements of said tubes, means includingsaid energy source and voltage divider networks for applying a staticbias to said control grids, means for applying D.C. potentials to saidplates from said energy source, an energy storing device connectedbetween each of said plates and said control grids, a sound responsivedevice adapted to generate electrical signals in accordance with soundsignals received thereby, a plurality of frequency selective electricalcircuit means including said amplifier-detector tubes for selectivelyapplying said electrical signals to said amplifier-detector tubes insuch a manner as to cause a rise in the D.C. potentials on said plateswhen sound signals of predetermined character are received by said soundresponsive device, and electrical connecting means between said energystoring device and said voltage divider networks for causing said risein D.C. potentials on said plates to de velop firing potentials on eachof said trigger tube control grids only when the D.C. potentials on saidplates each increase at a selectively predetermined rate.

20. In an underwater acoustic mine adapted to be launched from anaircraft in flight, the combination of a sound responsive deviceincluding at least one static element adapted to generate electricalsignals in accordance with sound signals received through thesurrounding water, a firing control channel controlled by saidelectrical signals and comprising a plurality of static ele mentsadapted to operate in a predetermined manner to fire the mine when soundsignals of predetermined character are received by said sound responsivedevice, and a protective channel controlled by said electrical signalsand comprising a plurality of static elements adapted to operate in apredetermined manner to prevent a firing of the mine when sound signalsof different character are received by said sound responsive device.

21. An acoustic mine firing control system of the character disclosedcomprising, in combination, a sound responsive device adapted togenerate A.C. signals in accordance with sound signals received thereby,a plurality of frequency selective channels actuated by said soundresponsive device, one of said channels including a first RC circuit, asecond RC circuit, means including said first RC circuit and controlledby said A.C. signals for producing a D.C. signal which reaches apredetermined value when sound signals of predetermined character arereceived by the sound responsive device for an interval of timeexceeding the time constant of the first RC circuit, a mine firingcircuit, and means including said second RC circuit and controlled bysaid D.C. signal for operating said firing circuit when the D.C. signalreaches said predetermined value and has increased at a faster rate thanthe discharge rate of the second RC circuit.

22. An acoustic mine firing control system of the character disclosedcomprising, in combination, a sound responsive device adapted togenerate A.C. signals in accordance with sound signals received thereby,a first RC circuit, a second RC circuit having a shorter time constantthan said first RC circuit, a third RC .circuit, a fourth RC circuithaving a shorter time constant than said third RC circuit, a firstelectronic circuit means including said first RC circuit and controlledby said A.C. signals for producing a first D.C. signal which reaches apredetermined value when sound signals within a first predeterminedfrequency range are received by said sound responsive device and reach apredetermined strength after an interval of time controlled by the firstRC circuit, a second electronic circuit means including said second RCcircuit and controlled by said A.C. signals for producing a second D.C.voltage which reaches a predetermined value when sound signals within asecond predetermined frequency range are received by the sound esponsi ede i e and a h a pr d ine en after an interval of time controlled by thesecond RC circuit, a mine firing circuit, a third electronic circuitmeans including said third RC circuit and controlled by said first D.C.signal for operating said mine firing circuit when the first D.C. signalreaches said predetermined value thereof and has increased at a fasterrate than the discharge rate of the third RC circuit, a fifth RCcircuit,

References Cited in the file of this patent UNITED STATES PATENTS Heapet a1 July 22, 19 19 Duffie Apr. 22, 1924 Barkley Feb. 8, 1944 FOREIGNPATENTS Great Britain Apr. 2, 1943

